1. Field of the Invention
The present invention relates to an imaging lens and an imaging apparatus. In particular, the present invention relates to a wide-angle imaging lens that is appropriate for use in an in-vehicle camera, a monitor camera, or the like that uses an imaging device, such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor). Further, the present invention relates to an imaging apparatus including the imaging lens.
2. Description of the Related Art
In recent years, the size of an imaging device such as a CCD and a CMOS became very small, and the resolution of the imaging device became very high. Therefore, the size and the weight of the main body of imaging equipment and an imaging lens mounted on the imaging equipment also need to be reduced. Meanwhile, imaging lenses used in in-vehicle cameras (on-vehicle cameras), monitor cameras (or surveillance or security cameras) and the like need to have excellent weather-resistance characteristics. Further, the imaging lenses need to have wide angles of view and excellent optical performance so that an excellent view is ensured for a wide imaging range.
Further, since it is desirable to reduce the cost for producing the imaging lens in the aforementioned fields, an optical system composed of a small number of lenses is desirable. Conventionally, for example, U.S. Pat. No. 7,280,289 (Patent Document 1), U.S. Pat. No. 7,551,373 (Patent Document 2), U.S. Pat. No. 7,405,890 (Patent Document 3), Japanese Unexamined Patent Publication No. 2008-268268 (Patent Document 4), and U.S. Pat. No. 7,697,221 (Patent Document 5) disclose imaging lenses, each composed of four lenses, in the aforementioned fields.
In the fields of in-vehicle cameras, monitor cameras, and the like, a demand for wider angle lenses increased in recent years. For example, a demand for lenses with full angles of view exceeding 200° increased. However, the full angles of view of lenses disclosed in Patent Document 1 are in the range of approximately 140° to 165°. The full angles of view of lenses disclosed in Patent Document 2 are 161° and 164°. The full angle of view of a lens disclosed in Patent Document 3 is 134°, and the full angles of view of lenses disclosed in Patent Document 4 are 150° and 159°. Further, the full angles of view of lenses disclosed in Patent Document 5 are in the range of approximately 140° to 146°. Therefore, they do not satisfy the demand for a wider lens with a full angle of view exceeding 200°.
Further, as the size of the imaging device became smaller, and the resolution of the imaging device became higher in recent years, there is a demand for an imaging lens that has high resolution and high optical performance that can make it possible to obtain excellent images for a wide image formation range. However, in the conventional lens system, it was difficult to satisfy such a demand, while structuring the lens system at low cost and in small size.